Effects of ethanol on Na+-dependent solute uptake in rabbit renal brush-border membrane vesicles

This study was undertaken to examine the effect of ethanol on Na+-dependent transport systems (glucose, phosphate, and dicarboxylate) in renal brush-border membrane vesicles (BBMV). Ethanol inhibited Na+-dependent uptakes of glucose, phosphate, and succinate in a dose-dependent manner, but not the uptakes of Na+-independent. The H+/TEA antiport was reduced by 8% ethanol. Kinetic analysis showed that ethanol caused a decrease in Vmax of three transport systems, leaving Km values unchanged. Ethanol decreased phlorizin binding, which was closely correlated with the decrease in Vmax of Na+-glucose uptake. These results indicate that ethanol inhibits Na+-dependent uptakes of glucose, phosphate, and dicaboxylate and that the reduction in Vmax of Na+-glucose uptake is caused by a decrease in the number of active carrier proteins in the membrane.

Increase of intracellular Ca2+ concentration by Vibrio vulnificus cytolysin in rat platelets; triggering mechanism of platelet cytolysis

Vibrio vulnificus cytolysin caused platelet cytolysis and increased intracellular calcium concentration ((Ca2+))i) of rat platelets in a concentration-dependent manner. In the presence of V. vulnificus cytolysin (3 HU/ml), lactate dehydrogenase (LDH) activity was increased from 1.3+/-0.4% of control to 64.3+/-3.4% in platelet suspension buffer. In Ca2+-free platelet suspension buffer, however, V. vulnificus cytolysin did not induce (Ca2+)i increase and LDH release. Addition of EGTA (2 mM) to suspension buffer after the initial Ca2+ influx reversed (Ca2+)i to the control level. However, a Ca2+ channel blocker verapamil (20 muM) or mefenamic acid (20 muM) did not inhibit V. vulnificus cytolysin-induced (Ca2+)i increase and LDH release. Divalent cations such as Co2+, Cd2+ or Mn2+ (2 mM each) also did not alter V. vulnificus cytolysin-induced (Ca2+)i increase and LDH release. V. vulnificus cytolysin (3 HU/ml)-induced calcium influx was completely blocked by lanthanum (2 mM). Lanthanum (2 mM) also completely blocked V. vulnificus cytolysin (3 HU/ml)-induced LDH release. Osmotic protectants such as, raffinose, sucrose or PEG600 (50 mM each) did not inhibit the lytic activity of V. vulnificus cytolysin. In conclusion, lanthanum sensitive Ca2+ influx plays a significant role in Vibrio vulnificus cytolysin-induced platelet cytolysis and thrombocytopenia in V. vulnificus infection.

Assessment of flavin-containing monooxygenase (FMO) activity by determining urinary ratio of theobromine and caffeine in a Korean population after drinking a cup of coffee

To examine individual variation in drug metabolism catalyzed by flavin-containing monooxygenase (FMO), 179 Korean volunteers' urinary molar concentration ratio of theobromine (TB) and caffeine (CA) was determined. Their urine was collected for 1 hr (between 4 and 5 hrs) after they drank a cup of coffee containing 115 mg CA and analyzed by an HPLC system. The lowest TB/CA ratio obtained was 0.40, the highest ratio was 15.17 (38-fold difference), and the median ratio for all subjects was 1.87. The mean was 2.66 with 2.36 S.D.. In 134 nonsmokers, the mean ratio was 2.35 +/- 1.93, that of 51 males was 2.30 +/- 2.26 and 83 females was 2.37 +/- 1.85, respectively. There was no significant gender difference in the obtained TB/CA ratio (Mann-Whitney test; p=0.518). There were no smokers among the 83 female volunteers. In the remaining 96 male subjects, the ratio obtained in 51 nonsmokers was 2.30 +/- 2.06 and that of 45 smokers was 3.62 +/- 3.19. This indicated that the TB/CA ratio was increased significantly in smokers (p=0.007). However, when the TB/CA ratios (FMO activity) obtained in all 179 Korean volunteers are compared with the urinary concentration ratios of paraxanthine (PX) plus 1,7-dimethylurate (17U) to CA (CYP1A2 activity), there was a weak but significant correlation (Pearson's correlation coefficient test; r2=0.28, p<0.0001). This indicates that, although the urinary TB/CA ratio mostly represents FMO activity, minor contribution by CYP1A2 activity cannot be ignored. In conclusion, the FMO activity measured by taking the urinary TB/CA ratio from normal healthy Korean volunteers shows marked individual variations without significant gender differences and the increased TB/CA ratio observed in cigarette smokers may have been caused by the increased CYP1A2 activity.

Comparative effects on secretion of LH, FSH, prolactin, and testosterone by chronic and direct hypothalamic administration of nonylphenol to adult male rats

Nonylphenol (NP) is a widespread environmental pollutant that has been shown to exert both toxic and estrogenic effects on mammalian cells. As the effects of NP on the reproductive system of adult male vertebrates are virtually unknown, we investigated not only the changes of reproductive hormone secretion in serum after chronic exposure to NP but also, in order to identify the site of its action, the reproductive hormone secretion in serum 48 hours after microinfusion of NP within hypothalamic preoptic area (POA). In the chronic exposure, the luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone in serum were decreased but prolactin (PRL) concentrations were increased. The LH, FSH, and testosterone in serum were decreased through the direct infusion of NP into POA, while there was no difference in mean serum prolactin between NP and control groups. These observations suggest that NP as endocrine disruptor has modulatory effects on hypothalamo-pituitary-gonadalaxis and that the site of action of NP could be hypothalamic POA.

Thyroid hormone-induced alterations of Ca2+-ATPase and phospholamban protein expression in cardiac sarcoplasmic reticulum

Alterations of cardiovascular function associated with various thyroid states have been studied. In hyperthyroidism left ventricular contractility and relaxation velocity were increased, whereas these parameters were decreased in hypothyroidism. The mechanisms for these changes have been suggested to include alterations in the expression and/or activity levels of various proteins; alpha-myosin heavy chain, beta-myosin heavy chain, beta-receptors, the guanine nucleotide-binding regulatory protein, and the sarcolemmal Ca2+-ATPase. All these cellular alterations may be associated with changes in the intracellular Ca2+ concentration. The most important regulator of intracellular Ca2+ concentration is the sarcoplasmic reticulum (SR), which serves as a Ca2+ sink during relaxation and as a Ca2+ source during contraction. The Ca2+-ATPase and phospholamban are the most important proteins in the SR membrane for muscle relaxation. The dephosphorylated phospholamban inhibits the SR Ca2+-ATPase through a direct interaction, and phosphorylation of phospholamban relieves the inhibition. In the present study, quantitative changes of Ca2+-ATPase and phospholamban expression and the functional consequences of these changes in various thyroid states were investigated. The effects of thyroid hormones on (1) SR Ca2+ uptake, (2) phosphorylation levels of phospholamban, (3) SR Ca2+-ATPase and phospholamban protein levels, (4) phospholamban mRNA levels were examined. Our findings indicate that hyperthyroidism is associated with increases in Ca2+-ATPase and decreases in phospholamban levels whereas opposite changes in these proteins occur in hypothyroidism.

Role of phospholipase A2 in oxidant-induced alteration in phosphate transport in primary cultured rabbit renal proximal tubule cells

The present study was undertaken to examine the role of phospholipase A2 (PLA2) in oxidant-induced inhibition of phosphate transport in primary cultured rabbit renal proximal tubule cells. Uptakes of phosphate and glucose were dose-dependently inhibited by an oxidant t-butylhydroperoxide (tBHP), and the significant inhibition appeared at 0.025 mM of tBHP, whereas tBHP-induced alterations in lipid peroxidation and cell viability were seen at 0.5 mM. tBHP stimulated arachidonic acid (AA) release in a dose-dependent fashion. A PLA2 inhibitor mepacrine prevented tBHP-induced AA release, but it did not alter the inhibition of phosphate uptake and the decrease in cell viability induced by tBHP. tBHP-induced inhibition of phosphate transport was not affected by a PKC inhibitor, staurosporine. tBHP at 0.1 mM did not produce the inhibition of Na+-K+-ATPase activity in microsomal fraction, although it significantly inhibited at 1.0 mM. These results suggest that tBHP can inhibit phosphate uptake through a mechanism independent of PLA2 activation, irreversible cell injury, and lipid peroxidation in primary cultured rabbit renal proximal tubular cells.